In recent years, development has been in progress on soft ionization such as matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI). Along with this, mass spectrometry has been increasingly used to analyze biopolymers such as proteins and peptides.
At present, tandem mass spectrometry (MS/MS: mass spectrometer/mass spectrometer) is widely used to analyze the structures of such biopolymers. According to the tandem mass spectrometry, generally, two mass spectrometers are connected to each other. The first mass spectrometer selects ions having a predetermined mass-to-charge ratio (m/z), which ions are then directed into a collision room where they collide with a target gas and are dissociated (CID: Collision-induced dissociation). Then, the second mass spectrometer mass analyzes generated fragment ions to obtain structural information such as an amino acid sequence.
The target gas used here is generally an inert gas. Note however that, in a few cases, an alkali metal vapor is used as a target gas. Examples of such a case are disclosed in for example Non Patent Literatures 1 to 3.